This invention relates to electromagnetic projectile launchers and more particularly to multiple bore launchers in which the conductors of a fired bore serve as augmenting conductors for subsequently fired bores in order to maintain a substantially constant muzzle velocity for each successively fired projectile as the firing current decreases.
Rapid firing electromagnetic projectile launcher systems have been proposed in which kinetic energy is stored by revving up a rotor of a kinetic energy storing generator. A fraction of this stored energy is then delivered for each acceleration of a projectile in such a manner that the firing current remains consistent for each shot, thus resulting in a uniform projectile muzzle velocity. Two types of systems have been deemed feasible, one involved a homopolar-inductor combination and the other a rotating pulse generator.
In the homopolar-inductor system, a homopolar generator charges an inductor to the firing current level, and suitable switching fires a projectile. This type of operation is described in commonly assigned copending application Ser. No. 256,745, filed Apr. 23, 1981, where some or all of the inductive storage is provided by bore flux augmenting conductors.
With the rotating pulse generator system, the generator produces distinct voltage pulses. In its simplest version, such a generator is connected to the breech rail terminals and, if the breech electrical loop is shorted by the presence of a projectile package, that projectile will be fired because the voltage pulse in combination with all the circuit and projectile-rail parameters results in the desired and consistent accelerating current variation. Barrel and bore configurations particularly suitable for use with a pulse generator are disclosed in commonly assigned copending application Ser. No. 256,745, filed Apr. 23, 1981.
Both the homopolar-inductor and the pulse generator systems have the desirable feature of being able to store sufficient kinetic energy for many shots in a relatively compact, rotating generator. They both suffer the disadvantage that fully charging the rotating machine with sufficient energy for a maximum length burst may take two or three minutes and thus, for immediate fire capability, in a battle tank for example, the rotating machinery may have to remain revved up for hours, though not necessarily at the full speed and hence full kinetic energy level. A further drawback of both systems is that the firing rate will tend to decrease for successive shots, though this can be improved by auxiliary equipment or circuitry. In addition, both systems have high stator reaction torques during inductor discharging or firing. Although this can be alleviated by using two counter-rotating rotors for the kinetic energy storage generator, this in turn increases the generator size, weight and cost and complicates the system for accelerating the rotors.
The present invention includes an inductive store and barrel system combination wherein the energy for launching a succession of shots is delivered directly by the inductive store without necessarily supplying any additional energy to that inductive store during the burst sequence. For example, the inductive store may, in the conventional manner, be charged to the desired first shot current level by a homopolar or other type of dc pulse generator and that generator may also remain connected to the inductive store during the firing sequence and thus may even continue to supply some additional energy during the burst. However the generator does not and normally cannot supply sufficient energy to maintain anywhere near constant current for very rapid successive launchings. The inductor-barrel system combination of this invention will result in a significant decrease in average launching current for each successive shot of a burst, while maintaining substantially constant muzzle velocity for each projectile of the burst.
The instantaneous accelerating force on a projectile in a parallel rail electromagnetic launcher is equivalent to 1/2L'I.sup.2, where L' is the barrel inductance gradient and I is the driving current. The average accelerating force in the bore, assuming L' to be constant from breech to muzzle, is then 1/2L'I.sup.2.sub.RMS. If the current decreases for successive shots, L' must then be made to correspondingly increase because the requirement of maintaining constant exit velocity can only be met by keeping the product L'I.sup.2.sub.RMS constant for successive shots. Although this constant muzzle velocity requirement can also be met by changing the barrel length or projectile weight for successive shots, neither of these alternatives appears practical. Thus it is required to increase L' for successive shots. In the present invention, this is accomplished by maintaining current flow in each previously fired bore and letting that current flow sufficiently augment the bore flux for successive shots, thereby providing the correct increase in inductance gradient L' to yield the same driving force at the now lower value of I.sup.2.sub.RMS. This operating scheme thus requires a number of bores equal to the maximum number of shots in a burst and the conductors of the first firing bore must continue to conduct current during the burst sequence. To prevent energy wastage and overheating of bore conductors, the burst firing should be extremely rapid with the interval between exit of one projectile and commencing acceleration of the successive one being preferably only or even less than one or two milliseconds. In accordance with this invention, the firing of each successive shot may be initiated by suitable switching or, alternatively, successive firing may be self initiated or self switched.
Launchers constructed in accordance with the present invention possess the important feature that all energy for a burst can be inductively stored. When a normally conducting inductor coil is used, charging that inductor to the required current level can be performed by a pulse dc generator, and this charging, which should take a fraction or in the order of a second, must absolutely be performed immediately prior to firing. However, if superconducting inductive storage is employed, the launch energy can be effectively stored for very long periods of time without energy addition, without high velocity rotating machinery, and during the firing, no reaction forces due to generator rotor torque will be produced. The size of a suitable superconducting inductive store is well under, on an energy stored basis, the size and weight of a kinetic energy storing generator together with its normally conducting inductive storage coil.